Mechanisms by which neuronal gene expression is regulated are potential sites for information storage in the brain, possibly helping to store information about brain exposure to drugs underlying features of tolerance and dependence. Such mechanisms involve DNA "cis" acting elements and DNA binding protein "trans" acting factors. To identify the cis acting regions of neurotransmitter genes, transgenic mouse with specific DNA fragments inserted into its genome were produced. In initial work completed at the beginning of this FY, transgenic mice harboring a gene fusion with expression of a CAT reporter gene under the control of a 200bp fragment of the human enkephalin gene promoter yielded brain expression of CAT activity that changed in response to some, but not all, of the stimuli that increase expression of the endogenous wildtype gene. This study was the first to identify small regions of a gene sufficient to confer regulation of the gene's expression resulting from trans-synaptic stimulation. Analyses of mutants that rendered the human promoter region closer to consensus sequences for the cyclase responsive element (CRE) enhanced tissue specific expression patterns; the first example of mutagenesis enhancing expression. These workers have continued to estimate the upregulation of "trans acting" transcription factor genes' expression in dorsal horn cells that could account for the increased expression of preproenkephalin mRNA in these cells. Activity focused on members of the fos transcription factor family, especially fos B and c-fos, which do display patterns of stimulation-induced upregulation sufficient to render them candidates for involvement in these upregulatory processes. Data concerning transcription factor gene expression in neurons and Cis-acting elements involved in this regulation make these some of the best-characterized examples of trans-synaptic regulation in the nervous system, and provide the groundwork for more complex studies of mechanisms whereby brain activities and gene expression mechanisms mesh to reflect or could store information about prior drug use.